1. Field of the Invention
This invention lies in the field of seismic sources. More particularly, it concerns a seismic source in the class of "low-energy" seismic sources, wherein the impact energy is comparable to those provided by weight drop, gas guns, air guns, etc.
Still more particularly, this invention lies in the field of manually transportable seismic sources for use in areas which are completely inaccessible to motordriven vehicles.
2. Description of the Prior Art
Prior to about 15 to 20 years ago, the basic type of seismic source was an explosive charge placed in a drilled shot hole.
At about this time, with the development and improvement of magnetic recording systems, which made possible the summation or stacking of plural repetitions of a seismic source, a number of surface seismic sources having a seismic energy output comprising a small fraction of the energy output of explosive charges were developed and were used in conjunction with suitable stacking apparatus. Of course, with the advent of digital seismic recording and processing, the step of stacking can be accomplished extremely easily. Thus many different types of low energy sources are used today. Some of the more common types are vibratory sources, gas guns, air guns, weight drops, and so on.
It is well known that in order to get improvement in the signal/noise ratio, the source even though it puts out a weak signal must still put out more than a certain minimum energy, related to that which is contributed to the received signal by the wind and other noise sources. Consequently, there is a minimum energy requirement for any practical seismic source which must be provided in order to be able to produce useful seismic stacked records.